Yes, public sex is illegal. It's called Public Indecency.
10 or so years ago the Supreme Court ruled that sex inside an enclosed car is not public
and therefore not illegal. They held that the interior of an enclosed
car is a private place.
The case that came before the court was concerning a couple having sex in an enclosed car with the windows closed, and I believe tinted, in an out of the way place. They were arrested and convicted. The case was appealed to the Supreme Court were they conviction was overturned. It seems like the case originated out of Texas but that may be wrong.
Having said that, there are a lot of criteria that must be met for a car to be considered private space: a convertible top must be up, the windows must be up... maybe tinted, and so on and so on. Those are the only ones I can think of.
Further, I think intent plays a part in determining public indecency in this scenario. That is, were you trying to conceal your actions or purposefully trying to expose yourself. Were you in an out of the way abandon place or driving along side a school bus where all the kiddies could look down and see what you were doing.
Lastly, what I've written about here was a court ruling from ten or more years ago that may have been overturned multiple times by now. Also, just cause the court says it's a private place doesn't mean your not going to have some cop arrest you and take you in anyway
. It just means you may get out of the fine and stay off the sex offenders list... after you pay your attorney several thousand dollars
. Then you still get to pay the public endangerment fine and the great big insurance rates.
I'm not going to be hypocritical and tell you not to do it. It's one of my favorite activities when my wife and I are on the road. Just use some common sense when you do it
. Stop and go traffic next to the school activity bus isn't the place.
There is no punishment. There is no reward. There are only consequences.